Method of manufacturing a submersible motor

ABSTRACT

A stator unit for an induction motor is encapsulated in a plastic and has an inner tubular lining which is coaxially aligned with the rotor bore through a set of bearings and bearing housing. The stator unit is fixed to a tubular unit frame, which is secured by adhesive in tenon grooves of upper and lower end frames. The upper end frame is secured by screws through holes in the upper bearing housing and end frame. In the method of assembly, the upper bearing is placed on an alignment fixture, which has pins adapted to fit the screw holes in the upper bearing housing and end frame. An arbor is inserted through the rotor bore of the upper bearing housing and through a corresponding bore in the end fixture and the upper end frame is placed over the arbor and fitted to the fixture pins. Then the stator unit is assembled over the arbor and into the tenon grooves of the upper end frame, where adhesive is applied. The lower end frame is similarly located on the other side of the motor, a clamping device is secured over the lower end, and the assembly is cured. The encapsulant is injected and after further curing, rotor and cover assemblies are substituted for the arbor and fixture.

United States Patent 1191 Lykes 1451 July 3,1973

[ METHOD OF MANUFACTURING A SUBMERSIBLE MOTOR [75] Inventor:RobertE.Lykes,Troy,Ohio

[73] Assignee: A. O. Smith Corporation,

Milwaukee, Wis.

22 Filed: Dec. 21, 1970 21 Appl. No.: 100,000

[52] US. Cl 29/596, 29/205 R, 310/42, 310/43, 310/87, 310/89 [51] Int.Cl. HOZk 15/00 [58] Field of Search 29/596, 205 R; 310/42, 43, 87, 89,90

[56] References Cited UNITED STATES PATENTS 3,571,921 3/1971 Pieper29/596 3,538,598 11/1970 Wightman et a1. 29/596 3,555,651 1/1971Latussek et a1 29/596 X 3,518,471 6/1970 Wightman et a1. 310/90 X3,135,884 6/1964 Luenberger 310/87 3,128,399 4/1964 OReilly 310/87Primary ExaminerCharles W. Lanham Assistant ExaminerCarl E. HallAttorney-Andrus, Sceales, Starke & Sawall [57] ABSTRACT A stator unitfor an induction motor is encapsulated in a plastic and has an innertubular lining which is coaxially aligned with the rotor bore through aset of bearings and bearing housing. The stator unit is fixed to atubular unit frame, which is secured by adhesive in tenon grooves ofupper and lower end frames. The upper end frame is secured by screwsthrough holes in the upper bearing housing and end frame. in the methodof assembly, the upper bearing is placed on an alignment fixture, whichhas pins adapted to fit the screw holes in the upper bearing housing andend frame. An arbor is inserted through the rotor bore of the upperbearing housing and through a corresponding bore in the end fixture andthe upper end frame is placed over the arbor and fitted to the fixturepins. Then the stator unit is assembled over the arbor and into thetenon grooves of the upper end frame, where adhesive is applied. Thelower end frame is similarly located on the other side of the motor, aclamping device is secured over the lower end, and the assembly iscured. The encapsulant is injected and after further curing, rotor andcover assemblies are substituted for the arbor and fixture.

8 Claims, 2 Drawing Figures PATENTEDJIJLB I973 3. 742.595

[NVENTOR ROBERT E LYKES ATTOR"'CVS METHOD OF MANUFACTURING A SUBMERSIBLEMOTOR BACKGROUND OF THE INVENTION This invention relates to a method ofassembling a dynamoelectric machine using an end alignment fixture incombination with a cylindrical alignment arbor to provide coaxialalignment of the stator and at least one bearing housing.

In submersible motors, the stator core and winding may be enclosedwithin a hermetically sealed casing to prevent contact between thestator winding and any liquid. This is necessary to prevent shortcircuiting of the winding. It is conventional to fill the statorenclosure with a thermosetting resin or other suitable filler plasticwhich sets to a hardened mass. The resin or like filler provides goodheat transfer from the winding to dissipate heat therefrom. The rotorgenerally need not be protected from liquid contact.

The stator casing conventionally includes a tubular lining which isconcentric with the rotor bore and the stator housing and whichseparates the stator unit from the rotor bore and rotor. It is alsoknown to secure the stator unit to the main frame or outer housing andto assemble this subassembly to the end frames.

In assembling a stator and rotor, it is important to obtain accuratecoaxial alignment of the stator with the rotor bore. Conventionally,this alignment is provided by precise machining of the end frames,bearing housings or the other parts which define alignment of the rotorbore. These machining processes are costly and time consuming.

Prior inventors such as Bemmann et al in U.S. Pat. No. 3,344,513 haveemployed arbors or mandrels which corresponded in size and shape to therotor bores. The stator assembly and various other parts may be alignedon the arbor and apertures in the stator assembly serve as locating fitsfor the bearing housings. The encapsulant, such as a thermosettingresin, which is provided in the stator winding space, serves to bond theend frames to the stator and main frame subassembly. This procedurehelps to avoid some of the machining, but still requires a relativelyprecise fit between the end frame and the main frame.

One inventor, T. G. Meyers in U.S. Pat. No. 3,256,590, achievesalignment of the stator unit and rotor bore by loosely fitting thestator units to the main frame in assembly, thus compensating for anynonalignment between the main frame of the other parts. His structurestill requires an accurate fit between the end frames and main frame ifthe end frames are to be located accurately. Further, the rotor boreaperture in his end frames must be relied on to assure coaxial alignmentof the bearing housing. Thus, in this method and apparatus, fullassurance of coaxial alignment still requires time consuming machiningand assembly procedures.

The primary problem, then, to which the present invention is directed,is to provide accurate coaxial alignment of all the machine parts whichdefine the rotor bore, and to accomplish this in the most simple andconvenient manner.

SUMMARY OF THE INVENTION The practice of the invention provides adynamoelectric machine with an encapsulated stator unit bonded to endframes with a main frame or housing loosely fitted and adhered to theend frames. This apparatus is advantageously assembled in accordancewith the invention to assure coaxial alignment of the stator and thebearing housings to define a precisely shaped rotor bore.

In the method of the invention, an arbor corresponding in diameter tothe rotor bore is inserted into an end alignment fixture. An upper endbearing housing is also fitted to the alignment fixture. For thispurpose, the fixture has pins disposed to be received into longitudinalholes for removably connecting an upper end frame to the bearinghousing. The bearing housing is thus coaxially aligned on the arbor andthe alignment fixture. The upper end frame is placed over the arbor andhas a corresponding longitudinal hole which fits the end frame to thepin that extends through the bearing housing from the alignment fixture.A stator unit-main frame sub-assembly is then placed over the arbor, andis aligned by reference to the arbor with the main frame loosely fittingwith a tenon fitting around the outside periphery of the upper end frameto fix the stator unitmain frame sub-assembly in coaxial alignment withthe rotor bore through the upper bearing housing. The loose fit of themain frame in the tenon fitting compensates for any eccentricity in thestator unit main frame sub-assembly.

A lower end frame and lower bearing housing is also placed over thearbor and clamped in place, with a similar tenon fitting in the lowerend frame receiving the lower end of the main frame.

In assembling a preferred form of the machine, a tubular liner isdisposed coaxially about the inner diameter of the stator unit and overthe arbor to seal the winding cavity which is filled with a plasticencapsulant material.

With the stator and lower end frame fixed, the alignment fixture, theupper bearing housing and the arbor and clamping device are removed andthe other usual machine parts are assembled to generally complete themachine.

By this convenient and reliable method of assembly, the invention thusassures precise axial alignment of the stator assembly, and bearinghousings with the rotor bore, while permitting practical tolerances inmachined parts of the assembly. This is accomplished without majorredesign or addition of parts to the usual machine design.

The drawings illustrate the best mode presently contemplated by theinventor for carrying out the practice of the invention.

In the drawings:

FIG. 1 is a side elevation of an electric motor of the invention withparts in section; and

FIG. 2 is a partially exploded side elevation of a subassembly of themotor in FIG. 1 with an alignment fixture and arbor in place and partsbeing in section.-

DESCRIPTION Illustrated in the drawings and particularly in FIG. 1 is asubmersible electric motor 1 having a conventional squirrel cage rotor 2carried on a rotor shaft 3. Shaft 3 is journalled for rotation atopposite ends within an upper sleeve bearing housing 4 and a lowersleeve bearing housing 5. I

Rotor 2 is rotatably supported by the bearings within the rotor bore ofan annular stator assembly 6. A tubular liner 7 is secured within thestator assembly 6 and seals the rotor bore from the stator.

Stator 6 includes a conventional, laminated annular magnetic core 8 andfield windings 9 inserted through longitudinal slots in the core. Inaccordance with the invention, stator assembly 6 is secured to agenerally tubular main frame it) to form a stator unit-main framesubassembly. Main frame 10 is attached as by a suitable epoxy to theouter surface of core 8 and therefore provides a direct heat conductivepath to the exterior for heat passage from the windings and core. Anupper end frame llll and a lower end frame 12, the latter of which maybe integrally formed with lower bearing housing 5, are included in themotor and are annular members with central bores coaxially aligned withrotor shaft 3 which extends through the central bores. The end frames 1l and 12 each have an annular tenon fitting 13, which may be a groove,on their inner peripheries corresponding generally to the position ofmain frame MI). The opposite ends of main frame llt) fit loosely intotenon fittings 13 where they are positioned and held by a suitablehardened epoxy or resin 14. The depth of epoxy 14 and the position ofthe ends of main frame 110 in tenon fittings 13 may be varied to provideprecise coaxial alignment of the stator unit-main frame subassembly withthe rotor bore and shaft 3.

At the upper end of motor 1, upper end frame 11 is connected to upperbearing housing 4 by means of a number of screws 15 threaded intoaligned longitudinal holes 16 and 17, extending respectively through anouter rim of bearing housing 4 and end frame 111. The fit between upperbearing housing 4 and the abutting edges of end frame 11 is notnecessarily precise, and the rotor chamber is sealed from the outside bymeans of an O-ring seal 18 between the end frame and the base of theouter rim of bearing housing 4.

Both end frames 11 and 12 have inwardly projecting annular flanges 19which extend in coaxial alignment with the rotor bore to the oppositeends of rotor 2. Tubular liner 7 extends beyond both ends of core 8 tofit generally loosely within a recess 2t and on the end inner surface ofeach flange 19. There, the liner 7 is fixed by means of a suitableadhesive in precise coaxial alignment with the rotor bore,notwithstanding any slight misalignment of the end frames. Rigidity ofthe stator assembly, end frames, main frame and liner assembly isprovided by a plastic encapsulant material 21, which fills the windingcavity defined by these parts. As well, the stator assembly is protectedfrom moisture by the encapsulant. Material 21 is a hardened plastic andpreferably a thermosetting resin which has good heat conductivity.Polyester and epoxy resins are suitable for this use.

Other, usual parts of motor ll include thrust components 22 disposed onshaft 3 in the rotor chamber between lower bearing housing 5 and thelower end of squirrel cage rotor 2. Attached across the central bore oflower bearing housing 5 and lower end frame 12 is a diaphragm 23 whichoperates in a chamber defined by a lower end cover 24. Screws 25 arethreaded through cover 24 into corresponding bores in lower end frame 5to secure cover 24 in place.

At the upper end, the motor chamber is sealed around shaft 3 by anannular seal 26 and protector assembly 27 which fits into acorresponding annulus in upper bearing housing 4. The motor windings areconnected to power by a series of leads 28, only one of which is shown,that extend through lead wells 29 in upper end frame 4 and throughencapsulant material 211 to their usual connections, not shown. Toprevent moisture seepage into the motor, wells 29 are filled with asuitable sealing material.

A conventional check valve 30 giving access through bearing housing 4 tothe rotor chamber is closed by a removable breather plug 31. Temporaryaccess to the winding cavity may also be needed, for purposes of addingthe encapsulant. Thus, an access opening 32 is provided in main frame 10and is closed by the plastic encapsulant.

To assemble motor 1, stator assembly 6 is confined within the generallyconcentric members comprising of main frame l0 and liner 7 to provide astator unit-main frame subassembly. This subassembly is positionedrelative to the bearing housings and end frames in accordance with themethod of the invention as described below.

Referring to FIG. 2, the stator unit-main frame subassembly is shown inposition on an arbor 33 which has a cylinder 34 shaped to the precisediameter of the desired rotor bore. Arbor 33 includes a central shaft 35which corresponds precisely to the position and diameter of rotor shaft3. Shaft 35 supports upper bearing housing 41 and an end alignmentfixture 36 on its upper end, which the fixture extending radially ofshaft 35 in precise coaxial alignment. Fixture 36 serves as an alignmentguide for upper end frame 11, and for that purpose has one or more guidepins 37 that fit into the longitudinally aligned holes 116 and 117.

As shown in FIG. 2 at the opposite or lower end of the stator unit-mainframe subassembly, there is located the lower end frame 12 with lowerbearing housing 5 ready for assembly on arbor shaft 35 which extendscoaxially of the rotor bore in the lower end. As detailed later, aclamping nut 38 is shown poised for assembly against frame 12 and ontothe threaded lower end of shaft 35.

An example of a method of assembly n accordance with the invention andemploying arbor 33 is to fit upper bearing housing 4 to alignmentfixture 36 by positioning guide pins 37 into holes 16. This ispreferrably a loose fit so as not to establish the precise coaxialalignment by means of the pins 37. The shaft 35 of arbor 33 is theninserted through the central bore of bearing housing 4 and correspondingbore of fixture 36. The fixture may be secured by suitable means such asa nut 39 threaded on the upper end of shaft 35 to tighten the fixture,bearing housing and arbor together.

With the bearing housing 4 in place at the upper end of the arbor, upperend frame lll is slipped over arbor 33 from the lower or opposite endand fitted against fixture 36 with pins 37 being inserted intolongitudinal holes 17. Then, the stator unit-main frame subassembly,including liner 7, is assembled over arbor 33 from the lower end,fitting the upper end of main frame it) into tenon fitting 13 of the endframe, and fitting the upper end of liner 7 into recess 20 of the upperend frame. Both fits are generally loose, permitting the subassembly tobe aligned coaxially with the rotor bore solely by reference to theouter diameter of arbor 34. Adhesive is applied in the upper tenonfitting 13 and recess 20 to fix this aligned position of the subassemblyand upper end frame.

it is convenient at this time to also assemble the leads 28 throughtheir wells 29 and connect them to the windings.

Lower end frame 12 may now be assembled on the other end of shaft 35,lower bearing housing 5 being, in this embodiment, integral with endframe 12, so that the sleeve bearing bore is coaxially aligned on shaft35. Similarly with the upper end, lower tenon fitting 13 and recess 20loosely receive the lower ends of main frame and liner 7 and adhesive isapplied at both joints while the stator unit-main frame subassemblyremains coaxially aligned on arbor 34. The assembly on arbor 34 issecured by threading clamping nut 38 on the lower end of shaft 35 untilit is positioned firmly against lower end frame 12.

Lead wells 29 may be filled with the sealant material at this time andthe entire assembly is cured on the arbor to harden the adhesive andfiller and fix the positions of the parts. Depending on the adhesivesand filler, the curing may be accomplished at room temperature or in aheated oven, not shown.

After the first curing, plastic encapsulant material 21 is injected inliquid form through access openings 32 to fill the winding cavities inthe stator unit-main frame subassembly. This may be done with anysuitable means such as a pump feed system from a storage tank, notshown. Openings 32 are closed by the encapsulant and the assembly isagain cured. In this example, the material 21 is a thermosetting resinand the assembly is cured in a heated oven, not shown, to harden theplastic. When cured, the stator assembly 6, main frame 10, end frames 11and 12 and liner 7 are all rigidly bonded in place by the encapsulantmaterial 21, while core 8 and windings 9 are encapsulated and protectedfrom moisture.

The cured assembly is then readied for assembly of the other parts ofthe motor. This is done by removing clamping nut 38, removing nut 39 andend alignment fixture 36, removing upper bearing housing 4, and slippingthe arbor 34 and shaft 35 unit out of the rotor bore. Now, rotor 2,shaft 3 and thrust components 22 are inserted into the rotor bore, withshaft 3 extending through the bore of lower bearing housing 5 and beinglocked in place in the conventional fashion. Diaphragm 23 and lower endcover 24 are then assembled to lower end frame 12.

The upper bearing housing 4 is now placed over the upper end of shaft, 3for reassembly, O-ring seal 18 being placed around the base of the outerrim of the housing to be wedged against the abutting surface of upperend frame 11 as the housing is positioned. Bearing housing 4 is fastenedby screws which are placed through longitudinal holes 16 and threadedinto longitudinal holes 17, which previously were fitted to pins 37 offixture 36.

Finally, seal 26 and protector assembly 27 is assembled over the outerend of shaft 3 and breather plug 31 is placed in the bore of valve 30 togenerally complete the assembly of motor 1.

By the use of arbor 33 and end fixture 36, the stator unit-main framesubassembly is conveniently and accurately aligned on the arbor andfixed in that position by adhesive at the tenon fittings 13. Since thetenon fittings permit play in connecting main frame 10 to the end frames11 and 12, the subassembly is aligned with reference to the arbor andprecise machining of parts is avoided.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims which particularly point outand distinctly claim the subject matter which is regarded as theinvention.

I claim:

1. In a method of assembling a dynamoelectric machine having a statorunit, a main frame secured to the stator unit, and an upper end frameand a lower end frame secured to opposite ends of the main frame, thestator unit and end frames defining a central generally cylindricalrotor bore; the steps comprising:

inserting a cylindrical alignment arbor corresponding in dimension tothe rotor bore through a bore of an end alignment fixture;

fitting the upper end frame over the arbor and onto the end alignmentfixture in coaxial alignment with the rotor bore;

assembling the stator unit and main frame over the cylindrical alignmentarbor; aligning the stator unit with reference to the arbor whileloosely fitting the main frame to the upper end frame, and securing themain frame to the upper end frame in the position required by the statorunit reference to the arbor; assembling the lower end frame on the arborafter securing the upper end frame, and securing the main frame to thelower end frame .in the position required by the stator unit referenceto the arbor; and

removing the arbor and alignment fixture, thereby leaving a subassemblyof the dynamoelectric machine which is precisely coaxially aligned withthe rotor bore. 2. In a method of assembling a dynamoelectric machinehaving a stator unit, a main frame secured to the stator unit, and anupper end frame and a lower end frame secured to opposite ends of themain frame and having tenon fittings corresponding generally to theopposite ends of the main frame, the stator unit and end frames defininga central generally cylindrical rotor bore; the steps comprising:

fitting the upper end frame on an end alignment fixture in coaxialalignment with the rotor bore;

assembling the stator unit and main frame over a cylindrical alignmentarbor which is coaxially aligned with the end alignment fixture andcorresponds in dimension to the rotor bore; aligning the stator unitwith reference to the arbor while loosely fitting the main frame intothe tenon fitting of the upper. end frame, and securing the main frameto the upper end frame in the position required by the stator unitreference to the arbor by applying adhesive in the tenon fitting:

assembling the lower end frame on the arbor followed by securing themain frame to the lower end frame in the same manner as secured to theupper end frame; and

removing the arbor and alignment fixture, thereby leaving a subassemblyof the dynamoelectric machine which is precisely coaxially aligned withthe rotor bore.

3. In a method of assembling a dynamoelectric machine having a statorunit, a main frame secured to the stator unit, an upper end frame and alower end frame secured to opposite ends of the main frame and aremovable bearing housing in coaxial alignment with the rotor bore whichis fixed to the upper end frame by at least one screw fitting throughaligned longitudinal holes in the bearing housing and the upper endframe, the stator unit and end frames defining a central generallycylindrical rotor bore; the steps comprising:

fitting the upper end frame on an end alignment fixture by fitting oneof said longitudinal holes to a pin provided by the end alignmentfixture for coaxial alignment with the rotor bore; assembling the statorunit and main frame over a cylindrical alignment arbor which iscoaxially aligned with the end alignment fixture and corresponds indimension to the rotor bore;

aligning the stator unit with reference to the arbor while looselyfitting the main frame to the upper end frame, and securing the mainframe to the upper end frame in the position required by the stator unitreference to the arbor;

assembling the lower end frame on the arbor with the main frame securedtothe lower end frame in the same manner as secured to the upper endframe; and

removing the arbor and alignment fixture, thereby leaving a subassemblyof the dynamoelectric machine which is precisely coaxially aligned withthe rotor bore. 4. In a methodof assembling a dynamoelectric machinehaving a stator unit, a main frame secured to the stator unit, and anupper end frame and a lower end frame secured to opposite ends of themain frame, the stator unit and end frames defining a central generallycylindrical rotor bore; the steps comprising:

fitting the upper end frame on an end alignment fixture in coaxialalignment with the rotor bore;

assembling the stator unit and main frame over a cylindrical alignmentarbor which is coaxially aligned with the end alignment fixture andcorresponds in dimension to the rotor bore;

fitting a tubular liner over the alignment arbor and within the statorunit;

aligning the stator unit with reference to the arbor while looselyfitting the main frame to the upper end frame, and securing the mainframe to the upper end frame in the position required by the stator unitreference to the arbor;

loosely fitting and securing one end of the liner to the upper end framewhile maintaining the liner in align-ment with the rotor bore byreference to the arbor;

assembling the lower end frame on the arbor followed by securing themain frame to the lower end frame in the same manner as secured to theupper end frame;

loosely fitting and securing the lower end frame to the other end of theliner while the lower end frame is being assembled to the main frame;

injecting a hardenable encapsulant plastic into and filling a' spacedefined by the liner, the stator unit, .the main frame and the endframes; and

removing the arbor and alignment fixture, therebyleaving a subassemblyof the dynamoelectric machine which is precisely coaxially aligned withthe rotor bore.

5. The method of claim 4 wherein the stator unit,

main frame and tubular liner are preassembled in a stator unit-mainframe subassembly, and wherein the subassembly is assembled over thearbor with the one end of the main frame loosely fitting into a tenonfitting of the upper end frame and the tubular liner loosely fitting theupper end frame; and the lowerend frame is similarly fitted to theopposite ends of the main frame and tubular liner.

6. A method of assembling a submersible electric motor having a plasticencapsulant stator-unit with a tubular core, an annular main framesecured to the outside diameter of the core, an upper end frame and alower end frame on opposite ends of the stator unit, a tubular liner onthe inside surface of the core, and bearing housings on opposite ends ofthe stator unit, the upper bearing housing being removable and attachedto the upper end frame by a screw through a corresponding longitudinalhole, and the bearing housings, liner and end frames defining a rotorbore; the steps comprising:

assembling the stator unit, the tubular liner and the main frame into asubassembly;

assembling the upper bearing housing on an end fixture having aninwardly projecting pin which is re ceived by said longitudinal hole inthe bearing housing, the end fixture having a central bore coaxiallyaligned with the rotor bore of the upper bearing housing;

inserting one end of an arbor through the upper bearing housing bore andend fixture central bore, the arbor being a cylindrical member havingthe shape of the rotor bore;

placing the upper end frame over the arbor and fitting the longitudinalhole of the end frame to the pin of the end alignment fixture;

assembling said subassembly over the arbor and aligning the subassemblyon the arbor, while loosely fitting one end of the main frame into atenon fitting of the upper end frame and loosely fitting one end of theliner to an inwardly projecting flange of the upper end frame;

applying adhesive between the main frame and tenon fitting and the linerand flange;

placing the lower end frame on the opposite end of the arbor and fittingthe lower end frame to the main frame and liner followed by securing thelower end frame to the main frame and liner similarly to the upper endframe;

assembling a clamping device on the arbor outside of the lower end frameand holding the assembled parts together on the arbor and end fixtureand curing the adhesive;

injecting a hardenable plastic into the spaces between said subassemblyand end frames to encapsulate the stator unit and bond said subassemblyto the end frames and curing the plastic;

removing the clamping device, the arbor and the upper bearing housing;

assembling motor parts in the rotor bore; and

replacing the bearing housing, whereby a submersible motor ismanufactured with a precisely aligned rotor bore.

7. In a method of assembling a dynamoelectric machine having a statorunit, a main frame secured to the stator unit, and an upper end framehaving a tenon fitting and secured to one end of the main frame, thestator unit and end frame defining a central generally cylindrical rotorbore; the steps comprising:

inserting a cylindrical alignment arbor corresponding in dimension tothe rotor bore through a bore of an end alignment fixture;

fitting the upper end frame over the arbor and onto the end alignmentfixture in coaxial alignment with the rotor bore;

assembling the stator unit and main frame over the cylindrical alignmentarbor;

aligning the stator unit with reference to the arbor while looselyfitting the main frame into the tenon fitting of the upper end frame,and securing the main frame to the upper end frame in the positionrequired by the stator unit reference to the arbor by applying adhesivein the tenon fitting; and

removing the arbor and alignment fixture, thereby leaving a subassemblyof the dynamoelectric machine which is precisely coaxially aligned withthe rotor bore.

8. In the method of claim 7, and including the steps of enclosing theend of said stator unitmain frame opposite to said upper end frame; and

injecting a hardenable encapsulant plastic into and filling the spacesbetween the alignment arbor, the stator unit, the main frame, the upperend frame, and the enclosure to the main frame end opposite to the upperend frame.

2. In a method of assembling a dynamoelectric machine having a statorunit, a main frame secured to the stator unit, and an upper end frameand a lower end frame secured to opposite ends of the main frame andhaving tenon fittings corresponding generally to the opposite ends ofthe main frame, the stator unit and end frames defining a centralgenerally cylindrical rotor bore; the steps comprising: fitting theupper end frame on an end alignment fixture in coaxial alignment withthe rotor bore; assembling the stator unit and main frame over acylindrical alignment arbor which is coaxially aligned with the endalignment fixture and corresponds in dimension to the rotor bore;aligning the stator unit with reference to the arbor while looselyfitting the main frame into the tenon fitting of the upper end frame,and securing the main frame to the upper end frame in the positionrequired by the stator unit reference to the arbor by applying adhesivein the tenon fitting: assembling the lower end frame on the arborfollowed by securing the main frame to the lower end frame in the samemanner as secured to the upper end frame; and removing the arbor andalignment fixture, thereby leaving a subassembly of the dynamoelectricmachine which is precisely coaxially aligned with the rotor bore.
 3. Ina method of assembling a dynamoelectric machine having a stator unit, amain frame secured to the stator unit, an upper end frame and a lowerend frame secured to opposite ends of the main frame and a removablebearing housing in coaxial alignment with the rotor bore which is fixedto the upper end frame by at least one screw fitting through alignedlongitudinal holes in the bearing housing and the upper end frame, thestator unit and end frames defining a central generally cylindricalrotor bore; the steps comprising: fitting the upper end frame on an endalignment fixture by fitting one of said longitudinal holes to a pinprovided by the end alignment fixture for coaxial alignment with therotor bore; assembling the stator unit and main frame over a cylindricalalignment arbor which is coaxially aligned with the end alignmentfixture and corresponds in dimension to the rotor bore; aligning thestator unit with reference to the arbor while loosely fitting the mainframe to the upper end frame, and securing the main frame to the upperend frame in the position required by the stator unit reference to thearbor; assembling the lower end frame on the arbor with the main framesecured to the lower end frame in the same manner as secured to theupper end frame; and removing the arbor and alignment fixture, therebyleaving a subassembly of the dynamoelectric machine which is preciselycoaxially aligned with the rotor bore.
 4. In a method of assembling adynamoelectric machine having a stator unit, a main frame secured to thestator unit, and an upper end frame and a lower end frame secured toopposite ends of the main frame, the stator unit and end frames defininga central generally cylindrical rotor bore; the steps comprising:fitting the upper end frame on an end alignment fixture in coaxialalignment with the rotor bore; assembling the stator unit and main frameover a cylindrical alignment arbor which is coaxially aligned with theend alignment fixture and corresponds in dimension to the rotor bore;fitting a tubular liner over the alignment arbor and within the statorunit; aligning the stator unit with reference to the arbor while looselyfitting the main frame to the upper end frame, and securing the mainframe to the upper end frame in the position required by the stator unitreference to the arbor; loosely fitting and securing one end of theliner to the upper end frame while maintaining the liner in align-mentwith the rotor bore by reference to the arbor; assembling the lower endframe on the arbor followed by securing the main frame to the lower endframe in the same manner as secured to the upper end frame; looselyfitting and securing the lower end frame to the other end of the linerwhile the lower end frame is beIng assembled to the main frame;injecting a hardenable encapsulant plastic into and filling a spacedefined by the liner, the stator unit, the main frame and the endframes; and removing the arbor and alignment fixture, thereby leaving asubassembly of the dynamoelectric machine which is precisely coaxiallyaligned with the rotor bore.
 5. The method of claim 4 wherein the statorunit, main frame and tubular liner are preassembled in a statorunit-main frame subassembly, and wherein the subassembly is assembledover the arbor with the one end of the main frame loosely fitting into atenon fitting of the upper end frame and the tubular liner looselyfitting the upper end frame; and the lower end frame is similarly fittedto the opposite ends of the main frame and tubular liner.
 6. A method ofassembling a submersible electric motor having a plastic encapsulantstator-unit with a tubular core, an annular main frame secured to theoutside diameter of the core, an upper end frame and a lower end frameon opposite ends of the stator unit, a tubular liner on the insidesurface of the core, and bearing housings on opposite ends of the statorunit, the upper bearing housing being removable and attached to theupper end frame by a screw through a corresponding longitudinal hole,and the bearing housings, liner and end frames defining a rotor bore;the steps comprising: assembling the stator unit, the tubular liner andthe main frame into a subassembly; assembling the upper bearing housingon an end fixture having an inwardly projecting pin which is received bysaid longitudinal hole in the bearing housing, the end fixture having acentral bore coaxially aligned with the rotor bore of the upper bearinghousing; inserting one end of an arbor through the upper bearing housingbore and end fixture central bore, the arbor being a cylindrical memberhaving the shape of the rotor bore; placing the upper end frame over thearbor and fitting the longitudinal hole of the end frame to the pin ofthe end alignment fixture; assembling said subassembly over the arborand aligning the subassembly on the arbor, while loosely fitting one endof the main frame into a tenon fitting of the upper end frame andloosely fitting one end of the liner to an inwardly projecting flange ofthe upper end frame; applying adhesive between the main frame and tenonfitting and the liner and flange; placing the lower end frame on theopposite end of the arbor and fitting the lower end frame to the mainframe and liner followed by securing the lower end frame to the mainframe and liner similarly to the upper end frame; assembling a clampingdevice on the arbor outside of the lower end frame and holding theassembled parts together on the arbor and end fixture and curing theadhesive; injecting a hardenable plastic into the spaces between saidsubassembly and end frames to encapsulate the stator unit and bond saidsubassembly to the end frames and curing the plastic; removing theclamping device, the arbor and the upper bearing housing; assemblingmotor parts in the rotor bore; and replacing the bearing housing,whereby a submersible motor is manufactured with a precisely alignedrotor bore.
 7. In a method of assembling a dynamoelectric machine havinga stator unit, a main frame secured to the stator unit, and an upper endframe having a tenon fitting and secured to one end of the main frame,the stator unit and end frame defining a central generally cylindricalrotor bore; the steps comprising: inserting a cylindrical alignmentarbor corresponding in dimension to the rotor bore through a bore of anend alignment fixture; fitting the upper end frame over the arbor andonto the end alignment fixture in coaxial alignment with the rotor bore;assembling the stator unit and main frame over the cylindrical alignmentarbor; aligning the stator unit with reference to the arbor whileloosely fitting the main frame into the tenon fitting of the upper endframe, and securing the main frame to the upper end frame in theposition required by the stator unit reference to the arbor by applyingadhesive in the tenon fitting; and removing the arbor and alignmentfixture, thereby leaving a subassembly of the dynamoelectric machinewhich is precisely coaxially aligned with the rotor bore.
 8. In themethod of claim 7, and including the steps of enclosing the end of saidstator unit main frame opposite to said upper end frame; and injecting ahardenable encapsulant plastic into and filling the spaces between thealignment arbor, the stator unit, the main frame, the upper end frame,and the enclosure to the main frame end opposite to the upper end frame.